1. Field of the Invention
The present invention relates generally to display of computer graphics. In particular, the present invention is directed towards a dithering technique for quickly displaying images at reduced color depth without significant quality loss.
2. Description of the Related Art
There is frequently a need to display an image on a display device that has insufficient color depth to display the image at its original color level. For example, a computer capable of an eight-bit color map will not accurately render a 16-bit image; a computer with a 24-bit color depth cannot display an image with 48-bit color, etc.
One way of displaying such an image is to cut off the lower-order bits of each pixel in the image. This, however, leads to the well-known problem of Mach banding, in which the human eye exaggerates the contrast between two surfaces with different luminance, making the image look unattractive.
Another attempt at solving the problem is the use of blue noise filtering. This is a collection of techniques in which pixels of different color are placed in some random fashion, in such a way that low frequency noise is suppressed and one is left with high spatial frequencies in the placement of the different colors. However, this technique causes clumps and gaps which, while minimized, are typically still visible. Secondly, so-called error diffusion, where some statistic propagates lexicographically across the image is not local—that is, the dither algebra depends on the environment of the pixel, which can require looking at each pixel several times in addition to being computationally expensive. Blue noise filtering is an error diffusion technique in which the color error and pixel placement is randomly distributed over an image.
A need remains for a technique for efficiently dithering an image that results in a high quality output image and does not require extensive computational power.